1. Field of the Invention
The present disclosure relates to a sheet reading apparatus for reading an image on a sheet while conveying the sheet.
2. Description of the Related Art
In recent years, an image reading apparatus such as a copying machine, a facsimile machine or the like, which is installed in a small office or a standard home, often includes an auto document feeder (ADF) with an image reading function. The image reading apparatus with an ADF picks up a sheet one by one from a sheet bundle placed on a document tray and conveys the sheet to a reading position. Then, an image on the sheet having conveyed to the reading position is read by a reading unit, which is waiting at the reading position. Upon completion of the reading, the sheet is delivered to a predetermined delivery position.
To achieve further reduction in the cost of the apparatus in the ADF, a feature employing a single driving motor for driving a driving system for conveying a sheet is increasing. The ADF with such a feature is configured, using a mechanical gear constitution, such that the sheet moving speed when the sheet is read is increased compared with that when the sheet is fed. The above configuring allows the ADF to appropriately establish space between a preceding sheet and a following sheet (distance between the sheets) when the sheet is continuously fed from the document bundle. For example, even when a distance between the preceding sheet and the following sheet is zero at the time of sheet feeding, the preceding sheet having passed through a feeding unit is conveyed for reading at a speed faster than a speed when the sheet is fed. Therefore, the distance between the following sheet and the preceding sheet becomes a predetermined distance at a time when the following sheet reaches a reading position.
In addition, there is a phenomenon in which the preceding sheet and the following sheet are overlapped and conveyed when picking up each sheet from the document bundle, which is caused by, for example, a type of the document, the combination of the document, and use environment (temperature, humidity etc.). The phenomenon is called “early jam”. When early jam occurs, it becomes difficult to establish distance between the sheets. When the distance between the sheets is too short, reading of the following sheet will not be prepared after the completion of the reading of the preceding sheet. Therefore, sheet conveyance is stopped. As a result, a user is required to perform a predetermined operation for releasing jam.
Japanese Patent Application Laid-open No. 2011-246244 discloses a document conveying device which comprises means to drive conveyance by a single drive motor and means to invert read document. Then, when the distance between the sheets is narrow, the document conveying device inverts the following sheet by an inverting means and reads the sheet. Thereby the distance between the sheets is established to prevent jam.
Even in a case where the distance between the sheets becomes short, the document conveying device does not stop conveying the sheet but continue the operation. However, this may cause early jam because picking up a sheet from a document bundle placed on the document tray is not possible. Assuming such case, there is a high probability that the feature of “not stop conveying”, disclosed in the Japanese Patent Application Laid-open No. 2011-246244, may have an adverse effect, or, it may increase the burden on a user.
In particular, description is given in a case where each sheet of the document bundle is not appropriately separated and the sheet is conveyed with partially or fully overlapped. In this case, the document conveying device disclosed in the Japanese Patent Application Laid-open No. 2011-246244 continue the reading operation to the end of the sheet, which may lead the user to determine that the reading is successfully completed. Therefore, the user fails to notice, on the spot, that there was a failure in normally reading each sheet of the document bundle. This leaves a problem that it becomes difficult to sort the sheet which is already read and the sheet which is yet to be read.
The object of the present disclosure is, in light of the above-mentioned problem, to provide an image reading apparatus which can easily sort sheets which are already read and sheets which are yet to be read when early jam occurs and sheet conveyance is stopped.